1. Field of the Invention
This invention relates to a cooling fan, more particularly to a cooling fan with curved V-shaped impellers.
2. Description of the Related Art
FIG. 1 illustrates a conventional centrifugal cooling fan 50 for a notebook computer (not shown) The centrifugal cooling fan 50 includes a casing 51 and a plurality of impellers 501 extending outwardly and curvedly from a hub 502 which is mounted rotatably in the casing 51. The root of each of the impellers 501 extends in an axial direction relative to the hub 502. Since the centrifugal cooling fan 50 is used for a notebook computer and is thus relatively small, the impellers 501 are relatively short. As a consequence, air flow in the region swept by the rotating impellers 501 is relatively small. Moreover, the centrifugal cooling fan 50 tends to generate a relatively large amount of eddy currents in the casing 51, which significantly reduces the air density of the air flow delivered by the fan 50.
FIG. 2 illustrates a conventional axial cooling fan 60 that includes a casing 61 and a plurality of impellers 601 extending outwardly and curvedly from a hub 602 which is mounted rotatably in the casing 61. Each of the impellers 601 is inclined relative to the axis of the hub 602. Since the casing 61 has a depth that is relatively short, the air flow introduced by the impellers 601 will impact the casing 61 and will bounce back and forth in the casing 61, thereby significantly reducing the cooling efficiency of the fan 60.
U.S. Pat. No. 6,318,964 discloses an axial cooling fan that includes a hub having interconnected first and second hub halves, and a plurality of first and second impeller halves. Each first impeller half extends outwardly from the first hub half. Each second impeller half extends outwardly from the second hub half, and is connected to a respective one of the first impeller half in such a manner that both the first and second impeller halves are inclined relative to the axis of the hub in the same direction. The cooling fan thus disclosed has the same disadvantage as the conventional axial cooling fan.
Therefore, the object of the present invention is to provide a cooling fan with a plurality of V-shaped impellers that are capable of overcoming the aforementioned drawbacks of the prior art.
According to the present invention, there is provided a cooling fan that comprises: a rotatable hub; and a plurality of generally V-shaped impellers that are angularly displaced from each other and that extend outwardly from the hub. Each of the impellers has first and second impeller halves that extend outwardly from the hub and that are connected to each other so as to form cooperatively an angle therebetween.